OROVILLE — After an extensive study, state health officials can’t say why the rate for pancreatic cancer in Oroville doubled during 2004 and 2005.

Their report concludes that the increase in cases could just be coincidence. It recommends continuing to monitor the rate of cancer in the area.

In 2007, a local woman reported to health officials that she believed a large number of people had been diagnosed with pancreatic cancer or died of the disease in the Oroville area.

State health officials looked into her claim and found that in 2004 and 2005, a total of 24 people in the Oroville area were diagnosed with that kind of cancer. In a typical two-year period, 12 cases of pancreatic cancer would be expected.

The high number of cases prompted an in-depth study by state health officials. County health officials worked on the investigation, also. A 37-page report on the study was released today.

Health officials tried to interview surviving cancer patients and the relatives of those who had died. The report said officials targeted the 24 cases from 2004 and 2005, as well as nine cases diagnosed in 2006. Of these 33 cases, 25 interviews were done.

The purpose of these interviews was to find common factors that might have caused the illnesses.

“Although a variety of possible environmental and occupational exposures were noted, none was consistently found among enough members of the group to explain the occurrence of the excess,” the report stated.

The woman who originally brought the cases to the attention of health officials suggested they might be linked to the Koppers Industries wood-treatment plant that was known to have caused chemical pollution.

The report states that only one of the 33 people had ever worked at the plant, and only two lived in the area that was evacuated during a 1987 fire at the plant.

“The demographic characteristics of the group were not unusual, and typical pancreatic risk factors were common, including: diabetes, family history of diabetes and cancer, particularly pancreatic cancer, and tobacco use,” the report stated.

“We performed an extensive field investigation and data review and found no common factor among the cases that could plausibly account for an excess of pancreatic cancers,” the report went on.

It said that with most community cancer clusters, specific causes are not found. “If the thousands of communities in the state are considered, it is almost certain that some will have higher-than-normal cancer rates by chance.”

The report stated, “We recommend continued monitoring of the occurrence of pancreatic cancer for the next few years to determine if the number of cases returns to within the expected range, as is suggested by the decline in more recent data, or whether an excess persists,” it stated.

Butte County Health Officer Dr. Mark Lundberg said he was glad the study had been done even if it didn’t find a reason for the spike in cases. The best outcome would have been to find a cause since then action could have been taken to eliminate it, he said.

If cancer numbers remain high, more studies will be done, he added.

A community forum on the Oroville pancreatic cancer investigation and the disease itself is planned from 6 to 8 p.m. on Wednesday at Oroville Hospital. The public is invited to this event, which is sponsored by the American Cancer Society, state Department of Public Health and the Butte County Public Health Department.

Staff writer Larry Mitchell can be reached at 896-7759 or lmitchell@chicoer.com.

BACKGROUND: Health officials have been looking into why the number of cases of pancreatic cancer in the Oroville area doubled during 2004 and 2005.

WHAT’S NEW: A report on the investigation released today found no explanation for the increase in cases.

WHAT’S NEXT: A public meeting to discuss the investigation and pancreatic cancer itself will be held Wednesday.